docs: def get_traceback(db, job_id):
      """
      Return the traceback of the given calculation as a list of lines.
      The list is empty if the calculation was successful.
  
      :param db:
          a :class:`openquake.server.dbapi.Db` instance
      :param job_id:
          a job ID
      """
      # strange: understand why the filter returns two lines or zero lines
      log = db("SELECT * FROM log WHERE job_id=?x AND level='CRITICAL'",
               job_id)
      if not log:
          return []
      response_data = log[-1].message.splitlines()
      return response_data